KVM: x86: Mark vmcs12 pages as dirty if and only if they're mapped

Mark vmcs12 pages as dirty (in KVM's dirty log bitmap) if and only if the
page is mapped, i.e. if the page is actually "active" in vmcs02.  For some
pages, KVM simply disables the associated VMCS control if the vmcs12 page
is unreachable, i.e. it's possible for nested VM-Enter to succeed with a
"bad" vmcs12 page.

Link: https://patch.msgid.link/20251121223444.355422-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/vmx/nested.c

@@ -3984,23 +3984,14 @@ static void vmcs12_save_pending_event(struct kvm_vcpu *vcpu,
 
 void nested_mark_vmcs12_pages_dirty(struct kvm_vcpu *vcpu)
 {
-	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
-	gfn_t gfn;
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
 	/*
 	 * Don't need to mark the APIC access page dirty; it is never
 	 * written to by the CPU during APIC virtualization.
 	 */
-
-	if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW)) {
-		gfn = vmcs12->virtual_apic_page_addr >> PAGE_SHIFT;
-		kvm_vcpu_mark_page_dirty(vcpu, gfn);
-	}
-
-	if (nested_cpu_has_posted_intr(vmcs12)) {
-		gfn = vmcs12->posted_intr_desc_addr >> PAGE_SHIFT;
-		kvm_vcpu_mark_page_dirty(vcpu, gfn);
-	}
+	kvm_vcpu_map_mark_dirty(vcpu, &vmx->nested.virtual_apic_map);
+	kvm_vcpu_map_mark_dirty(vcpu, &vmx->nested.pi_desc_map);
 }
 
 static int vmx_complete_nested_posted_interrupt(struct kvm_vcpu *vcpu)

include/linux/kvm_host.h

@@ -1381,6 +1381,7 @@ bool kvm_vcpu_is_visible_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
 unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn);
 void mark_page_dirty_in_slot(struct kvm *kvm, const struct kvm_memory_slot *memslot, gfn_t gfn);
 void mark_page_dirty(struct kvm *kvm, gfn_t gfn);
+void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
 
 int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gpa_t gpa, struct kvm_host_map *map,
 		   bool writable);
@@ -1398,6 +1399,13 @@ static inline int kvm_vcpu_map_readonly(struct kvm_vcpu *vcpu, gpa_t gpa,
 	return __kvm_vcpu_map(vcpu, gpa, map, false);
 }
 
+static inline void kvm_vcpu_map_mark_dirty(struct kvm_vcpu *vcpu,
+					   struct kvm_host_map *map)
+{
+	if (kvm_vcpu_mapped(map))
+		kvm_vcpu_mark_page_dirty(vcpu, map->gfn);
+}
+
 unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
 unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
 int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
@@ -1410,7 +1418,6 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, const void *data
 			      int offset, int len);
 int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
 			 unsigned long len);
-void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
 
 /**
  * kvm_gpc_init - initialize gfn_to_pfn_cache.